1. Field of the Invention
The present invention relates to an image forming method and dry toner useful for developing an electrostatic latent image formed by electrography, electrostatic recording, electrostatic printing or the like.
2. Discussion of the Related Art
A variety of methods using electrophotography for obtaining a recorded image have been disclosed in, for example, U.S. Pat. No. 2,297,691 and Japanese Patent Publications No. 49-23910 and 43-24748, incorporated herein by reference. Generally, these methods include the following steps:
(a) an electrostatic latent image is formed on a photoconductor by various methods; PA1 (b) the electrostatic latent image is developed with toner; PA1 (c) the developed toner image is transferred to a recording material such as paper or the like; and PA1 (d) the transferred toner image is fixed by application of heat, pressure or organic solvent vapor to obtain a recorded image. PA1 (1) an image forming apparatus using the one component developing method needs not have a toner concentration controlling device and therefore a cost efficient image forming apparatus can be manufactured; PA1 (2) a developing unit using the one component developing method needs only a small agitating device and therefore a compact image forming apparatus can be manufactured; and PA1 (3) life of the one component developer is relatively long. PA1 (1) fluorine-containing materials tend to be negatively charged when rubbed with toner because of their large negative polarity and therefore toner almost always charges positively and negatively charged toner can hardly be obtained; and PA1 (2) silicone resins have too poor durability to be applied to these members.
Methods of developing an electrostatic latent image are broadly classified into two types. The first type of the developing methods is a liquid toner developing method using liquid toner which is made by dispersing a pigment and/or a dye in an insulating organic liquid. The second type of the developing methods is a dry toner developing method which uses dry toner made by dispersing a coloring agent, such as carbon black or the like, in a binder resin, such as natural resins or synthetic resins. Currently, the dry toner developing method is widely used for electrophotography.
Further the dry toner developing method is broadly classified into two types. The first type of the dry toner developing method is a one component developer developing method using a one component developer (i.e., toner) in which, for example, both a coloring agent and a magnetizable substance are dispersed in a binder resin. The second type of the dry toner developing method is a two component developer developing method using a two component developer which includes a mixture of dry toner and a magnetizable carrier, such as iron powder or the like.
Between these two methods, the one component developer developing method is widely used for electrophotography because of the following advantages:
Further, the one component developer developing methods are broadly classified into two types. The first type of the one component developer developing methods is a one component magnetic developer developing method using one component magnetizable developer in which an electrostatic latent image is developed with one component magnetizable developer held on a magnetic developing roller. The second type of the one component developer developing method is a one component non-magnetic developer developing method in which an electrostatic latent image is developed with one component non-magnetizable developer which is supplied onto a non-magnetic developing roller by a toner supplying member.
In one component developer developing methods of both magnetic and non-magnetic developer developing types, when a developer (hereinafter referred to as toner) adheres on a toner carrying member in a developing unit and a toner film is formed on the toner carrying member, there occurs a problem in which waste toner collected at a cleaning section of the developing unit increases because of adhesion of toner on an area of a photoconductor which corresponds to the background of an image (hereinafter "adhesion of toner on an area of a photoconductor" referred to as "photoconductor fouling"). Since the waste toner does not contribute to the toner image formation, a fixed amount of toner packed in a toner container which is guaranteed to be able to develop more than a fixed number of copy sheets has to be increased, resulting in an increase of manufacturing cost. Therefore, the toner adhesion and the resultant film formation on the toner carrying member should be avoided.
In attempting to solve this problem, a toner film formation preventing method has been proposed in which a toner releasing material, such as fluorine-containing materials and silicone resins, is applied onto a toner contacting element of the toner carrying member. However, the method has the following drawbacks:
Therefore, these materials cannot be applied to the carrying member and a need exists for toner which does not adhere on a toner carrying member.
Further, a one component developer developing method can generally induce in toner less friction electricity than a two component developer developing method and accordingly a proper amount of a charge controlling agent is frequently added to the toner. For example, conventional positive charge controlling agents which make toner be charged with positive friction electricity include Nigrosine type oil soluble dyes, quaternary ammonium salts, azine dyes having an alkyl group, basic dyes and lakes thereof. Conventional negative charge controlling agents include metal-containing dyes, such as chrome-containing monoazo complexes, chrome-containing salicylic compounds, zinc salicylate compounds and chrome-containing organic dyes, such as copper Phthalocyanine Green and chrome-containing monoazo dyes.
However, when even the toner including these charge controlling agents adheres on a toner carrying member and toner film formation occurs on the toner carrying member, photoconductor fouling also occurs.
There is known a one component non-magnetic developer developing method in which an latent image formed on an electrostatic latent image carrying member is developed with a thin toner layer formed on a toner carrying member in a developing unit which includes the toner carrying member, and a toner layer regulating member and a toner supplying member in which the toner layer regulating member contacts the toner carrying member. In this one component non-magnetic developer developing method, toner tends to adhere on the toner carrying member and make a toner film thereon more frequently than in the case of the magnetic developer developing method. This is because toner is forced to be supplied to the toner carrying member using the toner supplying member in the one component non-magnetic developer developing method while the toner is supplied to the toner carrying member using a magnetic force of the toner carrying member in the one component magnetic developer developing method.
Japanese Laid-Open Patent Application No. 5-341556 appears to discuss a non-magnetic one component developer developing method which includes a non-magnetic toner carrying member feeding toner to an electrostatic latent image carrying member and a toner layer regulating member forming a toner layer on the non-magnetic toner carrying member wherein a metal oxide is included in the non-magnetic one component toner in an amount of from 20 to 50% by weight. This method improves reproducibility of half tone images but cannot improve toner film formation on the non-magnetic toner carrying member.
Because of these reasons, a need exists for toner for a one component developer developing method which has good image qualities and durability without contamination of developing apparatus such as toner film formation.